1. Technical Field
The present invention relates to an optical disk recording apparatus and an initial laser drive voltage calculation program capable of fast and accurately finding an initial laser drive voltage with reference to a target recording power at the time to start recording.
2. Related Art
A conventional optical disk recording apparatus finds a relational expression between a laser recording power and a laser drive voltage. Based on the relational expression, the apparatus determines the laser drive voltage to radiate the laser light set to the target recording power. The purpose is to shorten the time in which the laser recording power reaches a target recording power at the beginning of data recording. For example, the optical disk recording apparatus turns on a laser diode using two or more different preset recording powers. The optical disk recording apparatus detects a laser drive voltage at that time to find a relational expression between the recording power and the laser drive voltage. When the data recording starts, the optical disk recording apparatus configures a drive voltage based on the relational expression to set the laser recording power to a target value.
An optical disk recording apparatus has the laser diode control circuit (e.g., see patent document 1). This circuit stores a controls result of setting the recording power. After the next startup, the circuit reads the control result data for the previous recording power to configure the recording power. Such an optical disk recording apparatus is disclosed for example in Patent Publication No. 07-272305 (pp. 4 to 8, FIGS. 1 to 8).
However, the conventional optical disk recording apparatus turns on the laser to detect a laser drive voltage by forcibly turning off the focus servo to prevent recording on optical disks. Accordingly, the optical disk recording apparatus needs to reactivate the focus servo to start OPC (Optical Power Control). Extra time is needed before starting the OPC, thereby being incapable of fast starting the data recording.
The focus servo needs to be forcibly turned on or off, complicating programming for the optical disk recording apparatus.
As mentioned above, the optical disk recording apparatus turns off the focus servo to find the relational expression between the recording power and the laser drive voltage. The following problem exists. When a specified recording power is obtained from the relational expression, a laser drive voltage for the recording power differs from an actually recorded value.
FIG. 7 is a graph showing relationship between a laser diode drive voltage and recording power. When the optical disk recording apparatus radiates laser light to an optical disk by turning on the focus servo, reflected light partially also returns to the laser diode from the optical disk. Affected by this, the laser diode changes the luminous efficiency. When the optical disk recording apparatus radiates laser light to an optical disk while turning off the focus servo, almost no reflected light returns to the laser diode from the optical disk. The laser diode is free from the effect of the reflected light. For example, FIG. 7 shows a first case turning on the focus servo to allow return light and a second case turning off the focus servo to remove return light. Consequently, recording power Pw is subject to difference ΔP between the first and second cases, thereby causing the problem of making the recording power different from an actual value as mentioned above.